1. Field of the Invention
The present invention relates to a method for measuring dimensions of a fine pattern of, for example, integrated circuits (IC's) or semiconductors, etc. More precisely, the present invention relates to a method for measuring the dimensions of a fine pattern or patterns displayed on a display unit, such as a monitor TV by an optical image forming system.
2. Description of the Related Arts
In the manufacture of IC's or LSI's etc., it is very important to control the dimensions of fine patterns, for example, contact holes or through holes, etc., formed on a wafer of an IC or LSI, etc., in order to ensure that they conform to design dimensions, and thus produce high quality products.
The fine patterns, such as contact holes, are usually reproduced on an enlarged scale on a screen of a monitor TV by an optical image forming system. Namely, enlarged dimensions of the fine patterns are optically displayed on the TV screen.
In view of the technical difficulties in a process of manufacturing fine circular patterns (e.g. contact holes) using a so-called CAD (computer-aided design) system, the fine patterns are usually designed to be rectangular- or square-shaped, as is well known.
In practice, however, circular patterns are formed on the wafer, etc., in place of the intended angular patterns, mainly because of a limited resolving power of the optical system used, or a limited etching precision or development, during the wafer manufacturing process. Namely, it is impossible or next to impossible to exactly reproduce an angular fine pattern as designed.
It should, however, be noted that such an inevitable phenomenon, i.e., formation of the circular patterns contrary to the design, does not in itself cause serious impairment of the quality of the products, since the shape per se of the contact holes is not important, to the establishing of a reliable electrical connection through the contact holes.
When such circular shape fine patterns are displayed on the monitor screen by the optical image forming system, slightly collapsed or deformed circular images appear on the monitor screen, depending on a deviation of the optical axis of the optical system, or a deviation of a light beam emission from a light source or the like, causing the peripheral edges of the patterns to be blurred or uneven in particular, thus resulting in a formation of substantially elliptically shaped pattern images on the monitor screen. Namely, the circular patterns on the wafer are reproduced as elliptical patterns on the screen. This often occurs in practice.
The deviation or deformation of the pattern images on the monitor screen, which is mainly caused by a failure or inaccuracy of the positioning or adjustment of the optical image forming system, as mentioned above, results in incorrect dimensional measurement of the patterns.